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Mark 12D Problem???

I have been struggling with a radio problem for some time now and am
having a tough time finding the real "root cause"! (I have a Narco -
Mark 12D)

It started several months back, when I would occaisionally get a "stuck
mike". After several phases of trouble-shooting, it appeared to be a
problem with the audio panel, which was replaced and seemed to solve
the problem.

A month or so ago, I lost contact with ATC while shooting some practice
approaches... Apparently, they could hear me, but I couldn't hear them
(confirmed by using my hand-held). Ever since then, I have been having
strange issues with the radio, but it will occaisionally work fine for
20 minutes or so???

Symptoms:
1. No side-tone when transmitting???
2. Occaisional loss of reception on known frequencies
3. No response (on known frequencies) to transmissions

I took the radio into a Narco dealer and they confirmed a problem with
the transmission switch (replaced a diode) and yellow-tagged the radio.
I put the radio in the plane and it worked like a champ for about 30
minutes and started to exhibit the symptoms again??? I took it back to
the dealer and the bench tested it for a couple of hours and said that
it worked fine and everything was within specs! :-(

I'm worried about throwing good money after bad and don't even know
where to begin in resolving this issue. (I can't afford to throw a lot
of money at new avionics and would like to get what I have working, if
at all possible)

Does anybody have any recommendations at troubleshooting this problem?
My mechanic is at a loss as well. The loss of side-tone, while
transmitting, seems to be an interesting issue...

I had a similar with some of same symptoms, eventually eliminated the
problems by changing of audio panel.
Various radio shops never found a specific fault.
What audio panel do you have ?

Roy

"three-eight-hotel" wrote in message
oups.com...
I have been struggling with a radio problem for some time now and am
having a tough time finding the real "root cause"! (I have a Narco -
Mark 12D)

It started several months back, when I would occaisionally get a "stuck
mike". After several phases of trouble-shooting, it appeared to be a
problem with the audio panel, which was replaced and seemed to solve
the problem.

A month or so ago, I lost contact with ATC while shooting some practice
approaches... Apparently, they could hear me, but I couldn't hear them
(confirmed by using my hand-held). Ever since then, I have been having
strange issues with the radio, but it will occaisionally work fine for
20 minutes or so???

Symptoms:
1. No side-tone when transmitting???
2. Occaisional loss of reception on known frequencies
3. No response (on known frequencies) to transmissions

I took the radio into a Narco dealer and they confirmed a problem with
the transmission switch (replaced a diode) and yellow-tagged the radio.
I put the radio in the plane and it worked like a champ for about 30
minutes and started to exhibit the symptoms again??? I took it back to
the dealer and the bench tested it for a couple of hours and said that
it worked fine and everything was within specs! :-(

I'm worried about throwing good money after bad and don't even know
where to begin in resolving this issue. (I can't afford to throw a lot
of money at new avionics and would like to get what I have working, if
at all possible)

Does anybody have any recommendations at troubleshooting this problem?
My mechanic is at a loss as well. The loss of side-tone, while
transmitting, seems to be an interesting issue...

A classic connector symptom. "I took it out, put it back in and it worked
fine for half an hour, then crapped out again". You repositioned the
connector and it worked it's way back by vibration to it's normal
intermittent position.

Eliminate problems one by one. Does your audio panel have a bypass mode or
can you patch-pin around it to hardwire the radio into the aircraft system
and eliminate all the other radios? What other avionics are sharing the
audio panel wiring? Can you shut everything down except this ONE radio to
see if it really is the radio?

As to the Narco dealer replacing an intermittent diode ... hmmm ... never
yet found an "intermittent" diode in the last 50 years of designing and
fixing this stuff. The diode is good or it isn't. There isn't any
in-between. Intermittent solder connections ... thousands. Intermittent
semiconductor parts ... for all intents and purposes never.

Jim

"three-eight-hotel" wrote in message
oups.com...
I have been struggling with a radio problem for some time now and am
having a tough time finding the real "root cause"! (I have a Narco -
Mark 12D)

It started several months back, when I would occaisionally get a "stuck
mike". After several phases of trouble-shooting, it appeared to be a
problem with the audio panel, which was replaced and seemed to solve
the problem.

A month or so ago, I lost contact with ATC while shooting some practice
approaches... Apparently, they could hear me, but I couldn't hear them
(confirmed by using my hand-held). Ever since then, I have been having
strange issues with the radio, but it will occaisionally work fine for
20 minutes or so???

Symptoms:
1. No side-tone when transmitting???
2. Occaisional loss of reception on known frequencies
3. No response (on known frequencies) to transmissions

I took the radio into a Narco dealer and they confirmed a problem with
the transmission switch (replaced a diode) and yellow-tagged the radio.
I put the radio in the plane and it worked like a champ for about 30
minutes and started to exhibit the symptoms again??? I took it back to
the dealer and the bench tested it for a couple of hours and said that
it worked fine and everything was within specs! :-(

I'm worried about throwing good money after bad and don't even know
where to begin in resolving this issue. (I can't afford to throw a lot
of money at new avionics and would like to get what I have working, if
at all possible)

Does anybody have any recommendations at troubleshooting this problem?
My mechanic is at a loss as well. The loss of side-tone, while
transmitting, seems to be an interesting issue...

I've got a four-place intercom, that I was beginning to question, but
to be honest... I don't know what the heck I'm doing! ;-) I want to
jump in and start figuring this out, but I'm afraid of messing things
up. My mechanic is really cool and is working well with me to try and
figure this out, but I think he is over his head a little when it comes
to avionics.

I would like to figure out if I can route the radio directly to the
aircraft system, like you mentioned... I tried using the aircraft mike
and setting the audio panel to speaker, but it's so loud and difficult
to tell what's going on. I tried plugging my headset into the aircraft
plugs under the panel (not the intercom ones) and couldn't get that
figured out either. If I can get radio directly to those ports, I
could isolate the rest of the system... Any suggestions on how to go
about that? Based on the audio panel, provided in the link, there's
likely no bypass... would you agree?

Thanks again to both for your responses! The aviation community
continues to impress me and the web sure helps foster that community!

I have:
1) a stand-alone Mark 122 NAV with glideslope (not part of the radio
system)
2) ADF (Inoperable - receives but indicator is off)
3) four place intercom (generic - nothing fancy)
4) standard mode-C transponder (also not part of the radio system)

Pretty basic... Love to throw in a GNS 4 or 5 -30, but that's a
pipe-dream for now... (Single income/two kids :-)

On Tue, 5 Jul 2005 08:45:50 -0700, "RST Engineering"
wrote:
A classic connector symptom. "I took it out, put it back in and it worked
fine for half an hour, then crapped out again". You repositioned the
connector and it worked it's way back by vibration to it's normal
intermittent position.

Eliminate problems one by one. Does your audio panel have a bypass mode or
can you patch-pin around it to hardwire the radio into the aircraft system
and eliminate all the other radios? What other avionics are sharing the
audio panel wiring? Can you shut everything down except this ONE radio to
see if it really is the radio?

As to the Narco dealer replacing an intermittent diode ... hmmm ... never
yet found an "intermittent" diode in the last 50 years of designing and
fixing this stuff. The diode is good or it isn't. There isn't any
in-between. Intermittent solder connections ... thousands. Intermittent
semiconductor parts ... for all intents and purposes never.

Jim

I would tend to agree, they sould either work or die, but...!

We have 2x Narco 12D+ and one had an intermittent transmitt audio (and
sidetone) loss. We decided to leave it until the next service and use
the other set. That too became intermittent a couple of times, but not
at the same time. Just before being sent away they both decided to
fail on me at the same time.
I understand it was a known problem and due to a zener diode. Both
sets were repaired and have been working for 6 months.

It's not likely to be temperature related as it was during the winter
in Scotland.

"three-eight-hotel" wrote in message
roups.com...
I have been struggling with a radio problem for some time now and am
having a tough time finding the real "root cause"! (I have a Narco -
Mark 12D)

It started several months back, when I would occaisionally get a "stuck
mike". After several phases of trouble-shooting, it appeared to be a
problem with the audio panel, which was replaced and seemed to solve
the problem.

A month or so ago, I lost contact with ATC while shooting some practice
approaches... Apparently, they could hear me, but I couldn't hear them
(confirmed by using my hand-held). Ever since then, I have been having
strange issues with the radio, but it will occaisionally work fine for
20 minutes or so???

Symptoms:
1. No side-tone when transmitting???
2. Occaisional loss of reception on known frequencies
3. No response (on known frequencies) to transmissions

I took the radio into a Narco dealer and they confirmed a problem with
the transmission switch (replaced a diode) and yellow-tagged the radio.
I put the radio in the plane and it worked like a champ for about 30
minutes and started to exhibit the symptoms again??? I took it back to
the dealer and the bench tested it for a couple of hours and said that
it worked fine and everything was within specs! :-(

I'm worried about throwing good money after bad and don't even know
where to begin in resolving this issue. (I can't afford to throw a lot
of money at new avionics and would like to get what I have working, if
at all possible)

Does anybody have any recommendations at troubleshooting this problem?
My mechanic is at a loss as well. The loss of side-tone, while
transmitting, seems to be an interesting issue...

I really prefer to troubleshoot, but the implication in your posts is that
you aren't "into" technician level electronics. If I've mischaracterized
you, I'll go at it from another route.

First, get yourself a can of tuner/control cleaner (Radio Shack 64-4315).
Do NOT use generic WD-40 or other petroleum based cleaner. You don't want
to leave a greasy residue AND you don't want to cob up the high frequency
characteristics of the connector(s). Mark 12D ... let me recollect ...
there are three or four versions of connector used on the 12D. Most
probably, since you have some sort of Cessna audio panel you have the
12D/Cessna version with the square block "Winchester" style connector.

It doesn't really matter. Use a very small amount of the cleaner on both
the radio connector and the tray connector. While the cleaner is still wet,
insert, pull, reinsert, pull, reinsert the radio half a dozen times.

Report results.

BTW, what model audio panel and model intercom do you have?

Jim

"three-eight-hotel" wrote in message
oups.com...
Sorry... Forgot to respond to other question...

I have:
1) a stand-alone Mark 122 NAV with glideslope (not part of the radio
system)
2) ADF (Inoperable - receives but indicator is off)
3) four place intercom (generic - nothing fancy)
4) standard mode-C transponder (also not part of the radio system)

Pretty basic... Love to throw in a GNS 4 or 5 -30, but that's a
pipe-dream for now... (Single income/two kids :-)

I beleive you are probably on to something with the connection
diagnosis... Vibration would be a great explanation to the 30 minutes
of working, then failure. I thought heat might have had something to
do with it to, but sometimes it fails at first attempt of using it.

I will try your suggestion and report back... (It may be a day or two)

I will also report back on models of audio panel and intercom I have.
(The second image in the link I sent "Figure 7-11 Used with Three
Transmitters" looks exactly like my audio panel, if it helps) The
intercom doesn't have anything indicative of a model on it, so I'll
have to poke around.

I bought the tuner/control cleaner yesterday and stopped at the airport
on my way into work this morning and did as you suggested... I sprayed
cleaner on the radio connector and tray connector and slid it in and
out half a dozen times. I then locked the radio into place (It seems
as though I got a better lock this time than I have in the past, as the
locking mechanism didn't seem to fall into place as well in the past)
I made a local "radio check" call and got a quick response of loud and
clear!

I won't be able to get out and fly it until probably Friday morning,
but will post back with the results. I just wanted to send a quick
update and let you know that I've got a good feeling about this!
Thanks for your help!

BTW - I checked out your website... Very nice! Looks like a lot of
cool products! I live in Garden Valley, near the Georgetown airport so
we are practically neighbors...